Field of the Invention
The present disclosure generally relates to a manufacturing method of a vessel. Specifically, the present disclosure relates to a manufacturing method of a pressure vessel with a heating device.
Description of Related Art
In conventional technology, a pressure vessel with heating device such as a storage water heater, solar energy water heater, pharmaceutical or chemical reaction vessel, brewing or food-processing vessel, etc. is usually in cylindrical shape and a heating device is placed inside the pressure vessel. As such, the cylindrical shape can satisfy the pressure bearing requirement while reducing the wall thickness of the pressure vessel. Placing the heating device inside the pressure vessel can help confine the thermal energy within the enclosed cavity of the vessel, to improve the heating efficiency.
Usually metal or, more recently, composite materials are used as the material for a pressure vessel to meet the requirements of both pressure bearing and thermal stability. Taking a pressure vessel made of metal for instance, the pressure vessel is usually built with three steel sections such as a top cap, a bottom cap and a cylindrical tube in between. These three steel sections are welded together to form the pressure vessel which is required to withstand at least 10 kg/cm2 of working pressure. The inner surface of the pressure vessel usually is coated with ceramic or glass coating, and is baked under the temperature of 800° C. to 900° C. to form a protective layer to prevent corrosion. In addition, an anode rod needs to be placed in the pressure vessel to prevent the corrosion of steel caused by hot water or other liquid. However, the anode rod would be depleted after 2 to 3 years, and the cost for replacement is high in order to maintain the corrosion resistance of the pressure vessel.
Taking a pressure vessel made of composite material for example, filament winding method is most commonly adopted to form the cylindrical structure of the pressure vessel. The basic concept of the filament winding method is to wind a continuous reinforced filament under tension over a rotating mandrel. Namely, the mandrel is inserted on a rotating spindle and the filament is wound around the rotating mandrel in a desired pattern or angle. The filament is impregnated in a bath with resin as they are wound onto the mandrel.
However, to form the vessel by filament winding method, the filament impregnated with resin has to be wound around the rotating mandrel till the mandrel is completely covered in multiple layers to the desired thickness, so the speed of manufacturing is relatively slow. Moreover, the mandrel is hard to remove after being covered by the filament impregnated with resin, so it usually stays within the pressure vessel as a part of the supporting structure, increasing the weight of the product. In addition, in many applications the material of the mandrel needs to be food-grade material with corrosion resistance and thermal stability, which increases the production cost.